94 PEOF. W. K. PAEKER OU THE STEUCTUEE OF 



The Endocranium of the Young Chameleon. 



The most striking things in this structure are the large, tumid, membranocranium 

 and the massiveness of the auditory capsules (Plate XV. figs. 1, 3, 4, 7, & 8). In front, 

 up to the optic passages (ii), the chondrocranium is merely an imperfect wall of 

 cartilage, confluent with the twin capsules of the nose. 



The occipital arch is well developed both above and below ; on its sides it is cramped 

 and narrowed by the ear-capsules ; the condyle {oc. c) is suboval transversely ; the bony 

 centres {e.o, b.o) barely reach it as yet. The foramen magnum (/. m) is very large, and 

 fairly at the end of the skull. The bones are well bordered by cartilage, all save a 

 space in front of the basal plate (fig. 2), where the floor is membranous ; that bone, the 

 basioccipital (S.o) is a large, thin, U-shaped plate, the horns of which enclose all but 

 the fore margin of the large suboval posterior basicranial fontanelle {p. b. c.f). A wide 

 tract of cartilage separates this threshhold piece from the side plates— the exoccipitals 

 {e.o) behind, and the opisthotics {op) further forwards. 



The exoccipitals (fig. 4, e.o) are narrow above and dilated below. The 9th and 10th 

 nerves (ix,x) pass between them and the opisthotics (o/.') ; and the 12th (xii) pierces the 



bone. 



There is a considerable tract of cartilage between the exoccipitals and the crown of 

 the arch, the superoccipital {s.o) ; this is to a considerable extent filled in by an exten- 

 sion, backwards, of the epiotic {cp), a shell of bone of the form of a quadrant (fig. 7, ep). 

 The supraoccipital has already sent upwards a squarish crest, rugged above ; this ends 

 in a rounded tongue of cartilage (fig. 8), which lies directly beneath the tongue-shaped 

 interparietal tract (fig. 4, i-p) ; afterwards, as I have shown, this will be a high thin crest 

 underpropping the high thin crest of the interparietal (Plates XVI. & XVII.). 



The outer view (fig. 7) shows the great triradiate synchondrosis between the three 

 periotic osseous tracts. These are very unequal in size : the prootic {pr-o) is the largest, 

 and is twice the size of the opisthotic {op), which again is twice the size of the epi- 

 otic. The ampullcB of the anterior and horizontal canals, and part of their arches, are 

 contained in the prootic. The ampulla of the posterior and the end of the horizontal 

 canals lie in the opisthotic ; and the meeting part of the anterior and posterior is in 

 the epiotic (Plate XVI. a. s. c, h. s. c,p. s. c,pr.o, op, ep). 



Below the arch of the horizontal canal, at the postero-inferor edge of the prootic, 

 there is an oval membranous space, the fenestra ovalis, filled by the stapedial end of 

 the columella (fig. 7,pr.o,f.o, st); the postero-inferior margin of the fenestra ovalis 

 is enclosed by cartilage, which will be ossified by the opisthotic, which constantly 

 forms the hinder edge of this space. The basisphenoid (b.s) is separated from the 

 antero-inferior corner of the prootic by a cartilaginous tract, and also, above, from 

 the horns of the basioccipital (fig. 8, b.s, b.o, pr.o). But below (fig. 2) the basi- 

 sphenoid sends back sharp horns of bone, which fasten on the ends of the broad horas 



